Teflon tape on pipe to clutch master cylinder union?

New master cylinder and new slave cylinder but the system's not holding pressure. I can hear the leak and it's up top. I was careful not to cross-thread when plumbed in the new master and the unions are tight. So I'm wondering what the next step is? Is there something I should use (teflon tape, perhaps) to help seal this up? Any help appreciated.

is it actually leaking any fluid, you either replsce the flare or the whole pipe if it isnt sealing

Cheers. Haven't filled it yet. Was pressuring it up with a pressured bleed system to check for leaks first. I can actually hear it hissing.

Well, put some fluid in it and see what the pressure bleed system can do for you. The seal between the pipe and the cylinder is created by the fact that the metals are slightly elastic, a bit like compression joints in domestic plumbing. So if the mating faces are good in the cylinder and on the pip on the end of the pipe, you should be able to get it to seal. The hissing could be from anywhere, including from round the cap. Get some juice in it and see what happens.

Soapy water in a hand sprayer is good for air leaks, but have to say working brake m/cyls or callipers dry isnt good for their long term health.

Thanks. If I get time tomorrow morning I'll fill the system as per Brown's suggestion and see what happens.

Be careful how much pressure you try pushing through with the bleeder kit as well.